"The American ambassador must consider himself very lucky that he is dealing with a professional army that the Zimbabwean national army is," presidential spokesman George Charamba told the state-run Herald newspaper.

Such action... was clearly intended to provoke an unwarranted diplomatic incident

Foreign ministry statement

"Elsewhere, and definitely in America, he would have been a dead man."

The Herald said Mr Dell had been arrested by a special presidential army unit when he entered a restricted zone in the botanical gardens, near President Robert Mugabe's official residence.

The Zimbabwean ministry of foreign affairs has protested to the US embassy about the incident, which took place on Monday afternoon.

"Such action was taken in a calculated disregard of the rules governing relations between states and was clearly intended to provoke an unwarranted diplomatic incident," it added.

The US mission said two senior Zimbabwean government officials had apologised for Mr Dell's detention and that it considered the matter closed.

Relations between the US and Zimbabwe have soured in recent years, with Washington accusing Mr Mugabe's government of rigging elections and abusing human rights.